Why a Black screen pop ups while playing games?

Whenever i play some games a blank screen appears for a second or two and goes. Its too annoying. While playing CS:GO it appears after 40 to 45 mins of playing and on gta 4 its like every after 10 to 15 mins. Whats causing this ? How do i stop this?Tried updating to latest gpu drivers, reinstalled windows. The temps are 45°C and 50°C for CPU and GPU respectively while playing. Any solution for this?

Is 300W PSU capable enough to fix this problem? Also my CPU &GPU temps were cool enough, right?so their temps weren't the problem, right? If buying a new PSU is the only solution then please suggest a good PSU as total wattage was around 130-150W (all components) , 300W PSU will do the work i guess.....